In lots of people's minds, the mystery of what killed the dinosaurs and other species — paving the way for the rise of mammals — was solved a couple of decades ago: a giant asteroid or comet slamming into the Earth, resulting in a dust cloud that shrouded the sun, cooled the planet dramatically and killed off plants and animals wholesale. It's a compelling story, but plenty of scientists never completely bought it.
A new book titled What Bugged the Dinosaurs, talks about how bugs that can spread disease were found in amber, against which dinosaurs wouldn't have had much resistance. The theory is that the dinos didn't all die in a massive epidemic; rather, the constant wear and tear of illness weakened the dinosaurs so that other catastrophes, like comets and volcanoes, could have finished them off.
This is combined with the Earth getting much warmer during a period called the Turonian, about 90 million years ago, when a "super-greenhouse" brought the ocean's surface temperature approached 100 degrees F, and alligators thrived in the Arctic.
note: this entry was totally plagarized from the referenced article due to the incredible laziness of the blog's "author". Don't like it? Well then my wife and I have saying for you: suck it.